1. Field of the Invention
This invention relates generally to ammunition and firearms and more specifically, to an improved combustible push rod used for launching tubular projectiles, the push rod being designed to sustain the gun barrel pressure and permit a high muzzle velocity for the projectile and yet be consumed by total combustion after the projectile leaves the gun barrel whereby to avoid potential foreign object damage to the platform of the gun such as an aircraft.
2. Prior Art
Tubular projectiles provide certain advantages over their non-tubular counterparts. Such advantages include a flatter trajectory, longer range, shorter flight time and superior penetration of the target. These advantages are derived principally from a significant reduction in the mass of the projectile as compared to non-tubular projectiles. Such reduction in mass along with certain aerodynamic design characteristics produces considerably less drag during the external ballistic cycle of the projectile. By way of example, one such advantageous tubular projectile is disclosed in U.S. Pat. No. 4,301,736 to Flatau et al issued Nov. 24, 1981. However, unlike non-tubular projectiles, the hollow configuration of tubular projectiles makes them inherently problematical in regard to applying high acceleration forces to the aft end of the projectile and in regard to maintaining the launching pressures within the gun tube which might otherwise be significantly reduced by the inadvertent passage of the gases produced by the burning propellants in the gun tube through the hollow center of the projectile. Solutions to this problem include some means for sealing the aft end of the projectile at least while it is in the gun tube and preferably until it attains the desired muzzle velocity. Such sealing means include pusher disks or pusher rods and sabots or some combination of these elements. By way of example, the aforementioned U.S. Pat. No. 4,301,736 discloses the use of a pusher disk which transmits the high acceleration forces from the propellant gases within the gun tube to the projectile and also discloses the use of a sabot which is designed to maintain the high pressure condition within the gun tube during the internal ballistic cycle. During the internal ballistic cycle tubular projectiles need a base or other certain device to seal one end of the hollow tube to sustain the gun barrel pressure and attain a high muzzle velocity. However, during the external ballistic cycle, the base has to separate from the projectile or be self-consumed in order to provide the projectile with a low aerodynamic drag to permit the benefit of the advantages of a tubular projectile.
When the tubular projectile is fired from an aircraft, a self-consumed base has to be used in order to avoid potential foreign object damage to the aircraft. One proposed solution to this problem is disclosed in U.S. Pat. No. 4,318,344 issued Mar. 9, 1982 to Price et al. This patent discloses a combustible sabot for use on spinning tubular projectiles. The disclosure maintains that prior combustible-type sabots were either too weak to maintain the pressure in the weapon barrel or burn too slowly at the pressure in the breech of the propellant powder or are too difficult or impossible to fabricate. The patent disclosure purportedly provides an invention which overcomes these prior art problems by providing a sabot which uses an epoxy anhydride binder compatible with and filled with energetic solid particles consisting of ammonium perchlorate, magnesium or aluminum, amorphous boron and molybdenum trioxide. Unfortunately, the combined installation and fabrication process relating to the integration of the sabot and the projectile is extremely complex and time consuming and therefore expensive. Furthermore, there is some question as to whether or not the epoxy base described in the Price et al patent is sufficiently strong to withstand the pressure exerted on it by the expanding weapon gases.
There is therefore a need for a self-consuming push rod for a tubular projectile which is structurally more capable of withstanding the internal ballistic process and which is relatively simple to fabricate as compared to the prior art. In addition, it is necessary to provide such a device which avoids gun barrel erosion otherwise caused by at least partial combustion of the push rod or sabot before the projectile has fully exited the gun barrel.